Systemic administration of drugs for the treatment of diseases can be effective, but may not be the most efficacious method for diseases which are localized within specific parts of the body. The controlled localized delivery of a drug to diseased tissue has become increasingly desirable because local administration of drugs can produce fewer side effects, and effective amounts of the drug will usually be smaller so the drug expense can be reduced.
Controlled localized delivery in body lumens can be difficult because the movement of bodily fluids through body lumens such as blood vessels and ducts can carry the drug away from the afflicted area.
Some methods of controlled local delivery of drugs involve inserting or implanting medical devices that include a polymer composition for release of a biologically active material. These polymer compositions may be applied to the surface as a coating. For example, various types of drug-coated stents have been used for localized delivery of drugs to a body lumen. An example is provided in U.S. Pat. No. 6,099,562 to Ding et al, and U.S. Pat. No. 6,238,121 to Yang et al. Such stents have been used to prevent, inter alia, the occurrence of restenosis after balloon angioplasty.
In at least some systems drug delivery is provided largely as a polymer coating degrades. This has the advantage that delivery profile over time should be a function of the polymer degradation rate. However, in practice it has been difficult to match a polymer degradation rate to a desired drug delivery profile.